The invention relates to an actuation unit for an electronically controlled hydraulic vehicle braking system with a brake booster which can be actuated by a brake pedal and which comprises a master cylinder and a reservoir for hydraulic fluid, with a first brake means which is coupled with, at least, a first vehicle wheel and which is connectable with the master cylinder via an electronically controlled valve arrangement in a basic position or, in an actuation position, is disconnectable from same, with a means for the simulation of the brake pedal behaviour, which is connectable with the master cylinder and which comprises a spring arrangement adapted to act against the hydraulic pressure from the master cylinder.
Such an arrangement is preferably used for so-called brake by-wire vehicle braking systems, wherein an electronically controlled pressure source (not explained in detail herein) builds up, holds and/or relieves the hydraulic pressure in the wheel brakes.
Such vehicle braking systems are, for example, known from DE 31 24 755 A1 or from DE 31 31 865 A1, respectively. These arrangements are, however, disadvantageous in that the brake pedal feeling, as it presents itself to the driver, and the behaviour of the brake pedal, as it is perceivable by the driver, only inadequately correspond to those of conventional vehicle braking systems.
The invention is therefore based on the object to avoid this drawback. To this end, the vehicle braking system according to the invention is developed in such a manner that a characteristics modeling means is associated with the spring arrangement.
The characteristics modeling means can also be arranged in the connection between the master cylinder and the means for simulating the brake pedal behaviour.
Alternatively, the characteristics modeling means can also be arranged in the connection between the means for simulating the brake pedal behaviour and a hydraulic reservoir.
In order to not unnecessarily supply the hydraulic pressure which can be provided by the master cylinder into the simulation means in the case of the first above described embodiment, a second valve arrangement can advantageously be arranged in the connection from the master cylinder to the means for simulating the brake pedal behaviour, by means of which the means for simulating the brake pedal behaviour can be disconnected from the master cylinder in a basic position or connected with same in an actuation position.
This applies analogously for the second above described alternative, wherein a second valve arrangement is preferably arranged in the connection from the means for simulating the brake pedal behaviour to the reservoir, by means of which the means for simulating the brake pedal behaviour can be disconnected from the reservoir in a basic position or connected with same in an actuation position.
In a presently preferred embodiment of the invention the means for simulating the brake pedal behaviour is formed by a cylinder/piston arrangement, wherein a piston is loaded by the spring arrangement which is formed as a helical spring or a diaphragm spring pack with a preferably progressive spring characteristic. Alternatively, the spring arrangement can also be formed by an elastomeric element, which as such is known from DE 43 43 386 A1.
The behaviour of the simulation means can be influenced by means of the characteristics modeling means depending on the direction of movement, the actuation force, and/or the actuation speed of the brake pedal.
To this end, the characteristics modeling means comprises at least one first throttle orifice which forwards hydraulic fluid upon the actuation of the brake pedal and one second throttle which forwards hydraulic fluid upon release of the actuation of the brake pedal. One check valve each is arranged upstream or downstream of the first and/or the second throttle.
In another embodiment of the invention a third throttle is connected in parallel with the first throttle which forwards hydraulic fluid upon the actuation of the brake pedal, with a pressure-controlled differential pressure valve being arranged upstream or downstream of same.
Further advantages, characteristics and properties of the invention will become apparent from the following description of the drawing.